There are mainly two different methods to do strength training and both have their inherent strengths and weaknesses. The first is to exercise with free weights and the second is to exercise with exercise machines that use cables to transfer the forces from a resistance source to a user.
The advantage of free weights is that they're very effective in producing strength gains and muscle mass. This is, in part, because the weight is unguided, and therefore secondary muscles get involved during the exercise in order to balance the weight. One of the inherent problems with free weights is that exercising with them is not as safe as exercising with an exercise machine. A lifter can lose his balance and be injured in a fall. The lifter may not be able to finish a lift, in which case he can become pinned under a bar. Plates can slide off the bar during a lift, potentially causing injury to the lifter and most likely to the floor. Lifting with free weights is also time consuming because of the need to take weight plates on and off to change the resistance, and because of the need to move the bar to different positions on the bar rack for different exercises. Also the lifting area can become cluttered with weight plates, thereby causing a hazard and making it difficult to locate desired weigh plates. In addition, some body parts are best worked out with an exercise machine, such as using a cable pulldown machine for working out the back. Furthermore, cost can be a factor. A lot of equipment is needed to be able to do a complete free weight workout, such as, the free weights, dumbbells, various lifting bars, a bench that inclines and declines, a bar rack for holding the barbell in several locations, and a cable pulldown machine. Purchase of all of this equipment can get quite expensive. Since free weights and free weight equipment are not designed to be compact or stored out of view, typically a whole room needs to be dedicated to such a setup.
Some of the advantages of exercise machines that make them so popular are because they overcome many of the disadvantages of free weights. They're safer to use than free weights as there is no risk of falling, of being trapped by the weights, or of having the weights fall off. Because the source of resistance is typically a weight stack where the weights are confined, the weights don't get scattered, lost, or dropped on the floor, and changing the amount of weight is quickly achieved by just changing the position of the selector pin. Many different exercises can be performed on one machine, and some exercise machines have multiple workout stations and weight stacks to permit performance of the various exercises needed for a complete body workout. Since it is possible to quickly and easily change between different exercises and resistance levels, circuit weight training is possible.
Circuit weight training was developed to promote both aerobic and muscular fitness at the same time. It consists of a series of exercises performed in succession, with a maximum of 30 seconds of rest between exercises, and lasting a total of 30 minutes. In order to maintain such a pace, an exercise machine must allow for a very quick and smooth transition between the different exercises and resistance levels, or there needs to be many different workout stations to allow all the different exercises needed to get a full body workout.
One of the problems with exercise machines is that they take up a lot of floor space. While some take up a smaller amount of floor space than others, typically they are all free standing and need to be set up far enough away from walls and furniture in order to allow for the space necessary to move around them and to exercise freely. Most exercise machines are designed such that only a certain number of body parts can be exercised per workout station. This is because the typical workout station is dedicated to doing specific exercises, such at a high pull station for doing pulldowns, or a low pull station for curls, or a station dedicated to doing the bench press or squats, etc. Exercise machines with these kinds of dedicated workout stations must have multiple workout stations for the user to get a full body workout. These larger machines require more steel, pulleys, and parts, resulting in a more complicated and expensive exercise machine that takes up more floor space.
Some inventions have attempted to deal with the problem of dedicated workout stations by allowing a set of pull points (the point at which individual hand grips or a bar is attached) to be adjustable in space. Some have achieved this by allowing the pull points to be adjusted vertically such as shown in U.S. Pat. Nos. 4,549,733; 4,603,855; and 4,898,381. One of the problems to be overcome by doing this is what to do with the excess cable as the pull points are moved. How complicated is the method for taking up the cable slack from moving the pull points? Another method to adjust the pull points in space is to position the pull points at the distal end of an arm, but the pivot of the arms is from a fix location that limits their versatility. Examples of this are shown in U.S. Pat. Nos. 4,826,157; 6,458,061 and 6,488,612. Cable length is constant but the arms pivot from a fixed pivot point.
For a lot of exercises a user may prefer to use a bar between the pull points. Some exercise machines that utilize pull points that move up and down are only designed to use individual hand grips. Some reasons a straight bar can't be used is because the vertical guides are spaced to closely together, the vertical guides aren't parallel to one another, and there is no space between the pull points (or arms) either because the arms are too short or there is structure directly between the pull points which prohibit the ability to do meaningful straight bar exercises like squats. Some examples of gyms that have one or more of these flaws are gyms like Nautilus NS700X, German patent application DE19801672, US patent application 2006/0116249, and Cybex FT-450. Some exercise machines have the ability to use a straight bar, like U.S. Pat. Nos. 5,725,459 and 6,447,430; and the Body Craft PFT Functional trainer, along with several others. The problem with these is that while they do allow the ability to use a straight bar between the pull points, there is no easy way to move the pull points at the same time while leaving the bar attached. They use spring loaded lock pins which require a constant force to keep the pins retracted during adjustment of the pull points. And so for these gyms there is no easy way to adjust the vertical position of the pull points except to remove the bar.
Another problem with exercise machines is that during the performance of some of the pressing exercises or fly motion exercises, the path of travel for the exercise follows a predefined arc or guide-way. Such single plane motion eliminates or substantially reduces the amount of work that smaller secondary muscles would be required to do to balance the weight if the same exercise was being performed using free weights.
Some machines require extra time in selecting a resistance level, especially those that utilize progressive resistance means such as springs, elastic band resistance, or flexible members to provide the resistance. These means of resistance are generally not as preferred by serious athletes for muscle development, who instead prefer the constant resistance offered by free weights or stack weight machines. Many of the functional exercise machines have two weight stacks instead of one which more than doubles the time required to change resistance levels. If a machine takes a long time to be setup for different exercises and resistance settings, circuit training cannot be performed, and the workout is longer than it would otherwise need to be.
Another problem with existing exercise machines is that they detract from a room that is not specifically dedicated for exercise. Most exercise machines aren't designed to be hidden from view when not in use, which can be unsightly for a room that is not specifically dedicated to be a fitness room. Some gyms are designed to fold up when not in use to cut down on the space they take up, but they're often too heavy and/or bulky to move or store away from view. There are some home gyms that fold up and can be stored out of sight, perhaps under a bed. But these require substantial time and effort to unfold for a workout and then fold up again afterwards. In addition, these fold-up gyms often fail to provide a full body workout.